Not applicable.
This invention is in the field of data communications, and is more specifically directed to modem data communications by way of a Universal Serial Bus (USB) peripheral device.
The present embodiments relate to universal serial bus (xe2x80x9cUSBxe2x80x9d) systems, and are more particularly directed to increasing the rate and flexibility of communications between a USB host and a peripheral.
USB is a recently-developed technology established by a joint effort of various: companies, resulting in an adopted standard set forth in Universal Serial Bus Specification, Revision 1.1, Sep. 23, 1998, which is hereby incorporated herein by reference. The USB Specification is directed to a goal of improving the user-friendliness of various aspects of computers and the peripheral devices typically used with such computers, and to this end governs many aspects about USB systems. In a USB system, peripheral devices are coupled to the host personal computer or workstation computer in a tiered-star topology over the USB bus; in this topology, external devices are physically connected to the USB bus by way of a standardized USB cable, rather than by way of specialized serial and parallel ports. The USB bus is mastered by a USB host, resident in the host personal computer or workstation, with the USB peripherals operating as slave devices on that bus.
The USB technology provides significant advantages to the computer system user, including the ability to connect up to 127 peripheral devices, in a xe2x80x9cdaisy-chainxe2x80x9d tiered-star topology, to a single USB port on the host computer. The USB technology also permits the user to connect and disconnect USB peripheral devices to or from the USB system without requiring system power-down, and generally with little or no configuration input required from the user. This capability provides considerable flexibility and possible cost reduction in comparison to many contemporary systems, particularly those which can only support one peripheral device per port. USB systems also can easily integrate various functions such as data, voice, and video, into the system through a single serial-data transfer protocol, without requiring add-on cards and the availability of their associated mainboard slots. Additionally, the master-slave arrangement permits the relatively high processing capacity of the host computer to perform and manage much of the data processing required for the peripheral function.
By way of further background, various techniques have been developed in the field of digital communications for routing messages among the nodes of a network. One such approach is referred to as packet-based data communications, in which certain network nodes operate as concentrators to receive portions of messages, referred to as packets, from the sending units. These packets may be stored at the concentrator, and are then routed to a destination concentrator to which the receiving unit indicated by the packet address is coupled. The size of the packet refers to the maximum upper limit of information that can be communicated between concentrators (i.e., between the store and forward nodes), and is typically a portion of a message or file. Each packet includes header information relating to the source and destination network addresses, permitting proper routing of the message packet. Packet switching with short length packets ensures that routing paths are not unduly dominated by long individual messages, and thus reduces transmission delay in the store-and-forward nodes. Packet-based data communications technology has enabled communications to be carried out at high data rates, up to and exceeding hundreds of megabits per second.
A well-known fast packet switching protocol, which combines the efficiency of packet switching with the predictability of circuit switching, is Asynchronous Transfer Mode (generally referred to as xe2x80x9cATMxe2x80x9d). According to ATM protocols, message packets are subdivided into cells of fixed length and organization, regardless of message length or data type (i.e., voice, data, or video). Each ATM cell is composed of fifty-three bytes, five of which are dedicated to the header and the remaining forty-eight of which serve as the payload. According to this protocol, ATM packets are made up of a number of fixed-length ATM cells; for the example of AAL5 protocol, the number of ATM cells in a packet is currently limited to a maximum of 1366 cells, corresponding to a maximum payload of 64 k bytes. The fixed size of the ATM cells enables packet switching to be implemented in hardware, as opposed to software, resulting in transmission speeds in the gigabits-per-second range. In addition, the switching of cells rather than packets permits scalable user access to the network, from a few Mbps to several Gbps, as appropriate to the application.
The ATM technology is particularly well suited for communications among computers over the worldwide and public medium commonly referred to as the Internet, because of the flexibility and recoverability provided by this packet-based approach. A relatively recent technology by way of which remote, home; or small office workstations can now connect to the Internet is referred to in the art as digital subscriber loop (xe2x80x9cDSUxe2x80x9d). DSL refers generically to a public network technology that delivers relatively high bandwidth, far greater than current voice modem data rates, over conventional telephone company copper wiring at limited distances. As such, DSL modulator/demodulators (xe2x80x9cmodemsxe2x80x9d) are now available for implementation with workstations and personal computers for ATM communications to and from the Internet, with data rates provided by DSL modems ranging from on the order of 500 Kbps to 18 Mbps or higher, according to conventional techniques.
Voice-band analog modems are, of course, well-known predecessors to the DSL modems noted above. Conventional voice-band modems communicate data by way of analog signals in the so-called voice-band, or audible frequencies, and support data rates up to 56 kbps according to modern protocols. While the DSL technology provides many important advantages relative to voice-band, including higher data rates and also the ability to simultaneously carry voice signals with the data communications, the DSL modem must be implemented within a specified distance (e.g., 18,000 feet) of a telephone system central office (that supports DSL services) or of a DSL repeater device; on the other hand, no such distance limitations are present for voice-band modem communications.
In the case of portable personal computers, the computer user may not always know whether he or she is presently within a DSL service area at any given point in time. As a result, portable personal computer users generally carry only a voice band modem (instead of carrying both a voice-band and also a DSL modem), foregoing the benefits of DSL modem communications in order to ensure their ability to effect data communications over their range of travel.
It is therefore an object of the present invention to provide a USB-based modem that may be configurable to operate in either voice-band mode or an ATM-based mode using Digital Subscriber Loop (DSL) technology.
It is a further object of the present invention to provide such a modem in which the segmentation and reassembly processes for ATM communications are accelerated when the modem is configured to operate in the ATM-based mode.
It is a further object of the present invention to provide such a modem that, when carrying out ATM communications such as over a DSL connection, more efficiently utilizes the USB bus for the communication of data than in conventional USB modems.
It is a further object of the present invention to provide such a modem in which facsimile transmissions may be carried out simultaneously with DSL data communications, and as separate facsimile sessions when the modem is configured to operate in the voice-band.
It is a further object of the present invention to provide such a modem in which voice-band data communications and facsimile communications are supported, in separate sessions.
Other objects and advantages of the present invention will be apparent to those of ordinary skill in the art having reference to the following specification together with its drawings.
The present invention may be implemented into a USB-based modem, within which circuitry for effecting modem communications by way of Asynchronous Transfer Mode (ATM) packets over a Digital Subscriber Loop (DSL) connection, or alternatively over a voice-band connection, may be carried out. A USB interface function controls communication between a processing device, such as a digital signal processor (DSP) and the USB host. The processing device, in turn, is connected to separate voice-band and DSL analog front-end functions, each of which is connected to the communication facility interface. For ATM communications over the DSL connection, ATM acceleration logic for segmentation and reassembly is embodied within the USB interface device. The host configures the operation of the USB interface device to select either DSL or voice-band communications; in the DSL mode, the ATM acceleration logic is enabled to perform the segmentation and reassembly functions, while in the voice-band mode, the ATM acceleration logic is disabled. A host interface controller is also provided in the USB interface device, operable in parallel with the ATM acceleration logic, enabling DSL communications to be carried out simultaneously with the receipt and transmission of facsimiles over the communication facility; the host interface controller also supports facsimile sessions when the modem is configured into the voice-band mode.